Luminescent tube



Aug. 14, 192s. 1,680,572

' R. H. RUNDLE LUIINESGENT TUBE y Filed Ilay 31, 1927 ATTORNEY Patented Aug. 14,- 1928.

UNITED STATES nor n. BUNDLE, or BUBLINGAME, aannemers.

LUMTNESCENT runs.

application mea my a1, 192?? seriai No. 195,324.

n Q l a o l\ Thls invention relates to improvements 1n luminescent tubes and more particularly to electrodes for luminous tubes using neon gas and mixtures thereof andv similar gasg Aeous media adapted to be rendered luminescent b electricaldischarges therethrough.

In t e present instance this invention will be described in connection with fits application to luminescent tubes'for sign purposes. In the use'of neon and similar gases in long tubes, great difficulty is experienced in properly evacuating the tubs of all occluded gases that may adhere tothe interior walls of the tube and the electrodes confined therein, before the luminiferous gas is introduced into the tube. After the introduction of the desired gas, ,f trouble is experienced from latentgases that mayem'anate from the electrodes asthey become heated by the electric discharges therebetween. Neon gas is highly sensitive to dilution, absorption and attenuati-on especiallyby gases that may be latent within the electrodes or given olf byA electrolysis, volatilization and distillation of g5 the electrodes after long usage. Such gases andgaseous mixtures vitiate the purity of the confined neon gas or other de ired medium. 'Theprinciple object of thi invention is to 'lower the cost of and speed up production and improve the product more especially-,by providing an electrode that will withstand the constant discharge of high tension 'electric current therefrom without deterioration or serious changes in its molecular structure,

,even at high temperatures; whereby the disfadvantages vabove set forth may be eliminated in the practice of this art. A further object of the invention is to construct the electrode of such material that it will with- 40 stand high temperature and maintain its integrity. f. Other objects and advantages will appear as this description progresses.

In this specification and the annexed drawings, the invention is illustrated in the form considered to be the best, but I do not wish' to be understood as confining. it to this formbecuseit may -be embodied in other forms, and it is also 4to be understood that in and by the claims following-the. descrip-A tion it is desired tocover the invention in whatsoever form it may be embodied.4

In the accompanying one sheet of ,drawings, Fig. lis a diagrammatic view ofl 1ummescent tube inlan electric circuit and b5 equipped with electrodesin accordance with this invention. Fig. 2 is a longitudinal sec- In det-ail the `construction illustrated in the drawings com-prises the conventional alternating current generator 1 suitably connected with the transformer 2, the high tension current from which is connected by the wires 3 and 4; with the electrodes within the electrode chambers 5 and 6 on opposite ends of the luminescent tube 7 This-combination of elements, with modifications to suit particular conditions, is in accordance with present practice. The novelty of this invention resides Within the electrodes, including their size; the ,materialfof which they are composed and their general structure.

In the past electrodes have been const-ructed of various metals, co per being the preferred metal in connection with neon gas.' Practice has roved that such electrodes must have a re atively. large area in order to carry the necessary high tension current at a relatively low temperature. In some previous instances the irreducible minimum of areao the electrode has been fixed at 1.5 square decimeters, about 15000 sq. m. m. per ampere, below which minimum the electrodes overheat and disintegrate, with deleterious effect upon the neon gas, as previously described. v v

, By the use of the present invention I have been able to reduce the area of the electrode to 13000 Sq. m. 1n. and "under favorable circumstances to much less per ampere of discharge. This I am able to accomplish by the novel construction and material ofwhich the electrode is composed, it being capable of withstanding temperatures up to incandescence, without deleterious effects upon the electrode and with beneficial results in purifying the tube prior to the introduction of the neon gas, and in maintaining its purity while producing the desired luminescence within the tube.

So far as I am aware, I- am the first to utilize in a luminescent tube, tungsten steel wire as now composed and drawn for use in connection withiincandescent lamps; and

to make use of an incandescent or nearly incandescent electrode within an evacuated tube,vprior to the introduction of neon gas or other luminiferous media therein to sea- 4son and prepare it 'for practical commercial purposes. Two very important advantages in the use of tungsten in this combination is, first, its long life in the presence of neon gas in a luminescent tube; and secondly, the advantage of raising the temperature of the electrode practically to iacandescence in the preliminary scavenging and seasoning or evacuation of the tube prior to the introduction of the neon. The high temperature materially aiding in rarefying and dislodging the occluded gases in cleansing the interior of the tube during the evacuation proeess, oven heating and annealing being dispensed with.

The cleansing or evacuation of the tube may be accomplished by any of the Well known processes for that purpose and is accomplis ed substantially as follows, see Fig. 1: A vacuum pump or other evacuating apparatus is attached to the by-pass 8 communicating with thev interior of the tube 7. The neon gas receptacle is also connected to this by-pass through the valve 9. The evacuation of the tube proceeds until a. low vacuum is attained that will permit of the heating of the electrode at opposite ends of the tube without oxidation or combustion of the same yet leave sufficient atmosphere to hold in pumpable suspension any impurities dislodged ivithin the tube. This condition is manifested by a slightly blue visible vapor within the tube. During the final stages of the evacuation of the tube, the electrode may be raised to incandeseence or nearly that temperature by the electric current passed therethrough. This temperature not only drives off o ccluded gases from the electrodes and the interior of the tube but also opens up the texture and releases any latent gases from the material of the electrodes, glass Walls or any substances therein that may later produce gases or gaseous effects deleterious to the desired gaseous Ymedia. After .the proper cleansing and evacuation of the tube is perfected as measured in the usual manner, theexhausting means is shut off at the valve 8. The gaseous medium is then permitted to fiow through the valve 9 into the interior of the tube in the usual manner. After-the desired quantity of gas, such as neon, 1s introduced into the tube as disclosed by the usual test, the by-pass 8 is fused off, completely sealing the gas Within the tube Z. A method of purifying the tubes by purging and a very good statement of conditions, useful in the practice of the art, is contained in the preamble of the United States Letters Patent to Machlett, 1,618,767, dated February 22, 1927. It is deemed unnecessary in the present disclosure to go into the purification or preliminary treatment of neon gas for use in luminescent tubes, for various purposes, since practically pure neon gas can be obtained in the open market.

The pair of electrodes required in the energizing of a luminescent tube may be alike in construction. For that reason, only one will be described. The electrode chambers, such as 5 6, comprise bulbous enlargements fused or Welded to the ends of the tube 7 as at the points 10-10. In the present inst-ance the electrode is supported by a tubular base 12 welded at 13 to the walls of the chamber 5. The terminal Wires 3 and 4 are welded at 14 to a short length 15 of duinet metal, the expansion and contraction co-efiicient 0f which is practically the same as that of the glass in which it is embedded. The tubular form of base is preferred because it prevents the short bending and breaking of the terminal Wires 3 4 where they are embedded in the supporting bases 12.

The electrode comprises a length of tungsten Wire as used in incandescent lamps as previouslyv stated. This wire is coiled into a helix as at 16 butt welded at 17 to the protruding end of the dumet metal 17, which then supports the helix in axial alinenient with the bore of the tube 7. The top coil 18 of the helix is bent into a continuous annulus and spirally joins the coil beneath, of thefhelix, this gives an unbroken discharge surface at the end of the electrode in proximity to the open end of the tube 7 where it joins the electrode chamber 5--6. Points or asperities on the electrode at this point, without the interposition of the coil 18, are liable to produce lateral discharges that may puncture the tube walls.

It is the present practice in the neon sign art to use glass tubing about seven-sixteenths of an inch internal diameter and of any length. For this the present preferred electrode 16 is composed of tungsten Wire as described, Which is about .O17 of an inch external diameter. Four and one-half inches of ivire is used in forming the helix 16, the coils of which are preferably about onequarter of an inch outside diameter, the helix being approximately one-half an inch long. The end' 18 should not be closer than one half of an inch from the adjacent entrance to the end' of the tube 7. The electrode chambers 5-6 are preferably about one inch in diameter.

These-various dimensions are given merely as an aid in the practice of this invention and are not to be construed as limiting the same since any one or all of them may be varied and their ratios, proportions and interrelations changed Without departing from the s irit of this invention, with suitable modi cations obvious to those skilled in this art, in meeting particular conditions. The means as described herein have proved in commercial practice the various advantages and effects set forth.

The use of the tungsten filament in the `electrodes, permits the simultaneous c leans- 111gl and seasoning of the tubes resulting inv` a great saving of time, and cost and an i-mproved quality of luminescent tube since ther preheat-ing is more uniform and manipulation 4reduced to the minimum.

The new method of cleansing the tubes in accordance with this invention is substan` tially as follows:v

When the electrode has been completely assembled it is connected to a manifold by means of pure gum rubber connection, the manifold being connected to a mercury vapor vacuum pump. A high tension current of approximately fifteen to twenty thousand volts is then passed through the electrodes heating the metal elements ofl same to incandeseence, thereb driving oifall the occluded that may ave been contained therein. intense heat is applied for a sullicient length of time to make absolutely sure that all the metal elements of the electrode havev been -thoroughly degased. The electrodes` are. then disconnected from the manifold and with a line air gun a salt solution is s rayed onto Athe metal elements of same ereby sea-1mg up the por ofthe metal and preventing vaporization. A sodium chloride solution for spra is preferred, but the same results obtained by using any one of several other `salt solutions having similar characteristics;

The temperature of theelectrode under normal operating conditions being approximately V400 degrees is low enough so that the salt. sprayoplaced on the metal elements of the electr es is not This methOd f 11: makes it unnecessary to further cleanse the -iixed my signature.

md"nymg' j' j sp BQYRBUNDLE.

elements of the electrode after it has b: in placed on the finished product. All the cleaning that is then necessary is to cleanse the vwalls of the done at a much ower temperature at the electrode than would otherwise be necessary.

As herein referred to luminescent tubesare distinguished by the presence therein of las`s itself which can be A gaseous media adapted to become luminous at low temperatures by the passage of an electric current. Incandescent tubes and bulbs are distinguishedby the presence therein of filaments rendered incandescent by the passage of the electric current. So far as I am aware it is novel to use such filaments in luminescent tubes.

Having thus described this invention what I claim and desire to secure byl Letters Patent is:

1. A luminescent tube having an electrode composed of tungsten iilament in the form of a helix, the end of said helix being bent into an annulus.

2. The method of cleansing and seasoning Y witness whereof I have-hereunto af- 

